1 files changed, 141 insertions, 0 deletions
diff --git a/src/auth.rs b/src/auth.rs
new file mode 100644
index 0000000..3926c70
--- /dev/null
+++ b/src/auth.rs
@@ -0,0 +1,141 @@
+use argon2::{password_hash::PasswordVerifier, Argon2};
+use axum::extract::State;
+use axum::{
+    body::Body,
+    http::{
+        header::{AUTHORIZATION, WWW_AUTHENTICATE},
+        HeaderMap, Request, StatusCode,
+    },
+    response::{IntoResponse, Response},
+};
+use base64::{engine::general_purpose::STANDARD as BASE64, Engine};
+use dashmap::DashMap;
+use password_hash::phc::PasswordHash;
+use std::{
+    collections::HashMap,
+    fs::File,
+    io::{BufRead, BufReader},
+    sync::Arc,
+    time::{Duration, Instant},
+};
+use tokio::sync::Semaphore;
+use tokio::time::sleep;
+
+fn load_users(path: &str) -> std::io::Result<HashMap<String, String>> {
+    let file = File::open(path)?;
+    let reader = BufReader::new(file);
+
+    let mut users = HashMap::new();
+
+    for line in reader.lines() {
+        let line = line?;
+
+        if let Some((user, hash)) = line.split_once(':') {
+            users.insert(user.to_owned(), hash.to_owned());
+        }
+    }
+
+    Ok(users)
+}
+
+#[derive(Clone)]
+pub struct AuthState {
+    idle_timeout: Duration,
+
+    users: Arc<HashMap<String, String>>, // user -> PHC hash string
+    cache: Arc<DashMap<[u8; 32], Instant>>,
+    /// Bounds concurrent Argon2 verifications (CPU and ~19 MiB each).
+    verify_slots: Arc<Semaphore>,
+}
+
+impl AuthState {
+    pub fn new(path: &str) -> Self {
+        let users = load_users(path).unwrap_or_default();
+
+        Self {
+            idle_timeout: Duration::from_secs(300),
+            cache: Arc::new(DashMap::new()),
+            users: Arc::new(users),
+            verify_slots: Arc::new(Semaphore::new(2)),
+        }
+    }
+}
+
+fn parse_basic(headers: &HeaderMap) -> Option<(String, String)> {
+    let encoded = headers
+        .get(AUTHORIZATION)?
+        .to_str()
+        .ok()?
+        .strip_prefix("Basic ")?;
+    let decoded = String::from_utf8(BASE64.decode(encoded).ok()?).ok()?;
+    let (user, pass) = decoded.split_once(':')?;
+    Some((user.to_owned(), pass.to_owned()))
+}
+
+async fn authenticate(state: &AuthState, headers: &HeaderMap) -> bool {
+    let Some((user, pass)) = parse_basic(headers) else {
+        return false;
+    };
+    let Some(hash) = state.users.get(&user).cloned() else {
+        return false;
+    };
+
+    let key = *blake3::hash(format!("{user}\0{pass}\0{hash}").as_bytes()).as_bytes();
+
+    // Fast path. The shard guard lives only until the end of this `match`;
+    // never call into the map while holding it.
+    let fresh = match state.cache.get_mut(&key) {
+        Some(mut last_seen) if last_seen.elapsed() < state.idle_timeout => {
+            *last_seen = Instant::now(); // slide
+            true
+        }
+        _ => false,
+    };
+    if fresh {
+        return true;
+    }
+
+    // Slow path: Argon2 is deliberately expensive, so keep it off the runtime
+    // threads and bound how many run at once.
+    let Ok(_permit) = state.verify_slots.acquire().await else {
+        return false;
+    };
+
+    let verified = tokio::task::spawn_blocking(move || {
+        PasswordHash::new(&hash)
+            .map(|ph| {
+                Argon2::default()
+                    .verify_password(pass.as_bytes(), &ph)
+                    .is_ok()
+            })
+            .unwrap_or(false)
+    })
+    .await
+    .unwrap_or(false);
+
+    if verified {
+        // Overwrites an expired entry; no separate remove needed.
+        state.cache.insert(key, Instant::now());
+    }
+
+    verified
+}
+
+pub async fn basic_auth(
+    State(state): State<AuthState>,
+    headers: HeaderMap,
+    request: Request<Body>,
+    next: axum::middleware::Next,
+) -> Response {
+    if !authenticate(&state, &headers).await {
+        sleep(Duration::from_millis(1500)).await;
+        return (
+            StatusCode::UNAUTHORIZED,
+            [(WWW_AUTHENTICATE, r#"Basic realm="Restricted""#)],
+            "Unauthorized",
+        )
+            .into_response();
+    }
+
+    next.run(request).await
+}